The present invention relates to a spanner that may prevent disengagement of fasteners during operation.
FIG. 1 of the drawings illustrates a conventional spanner with a box end. When in use, a nut (or bolt head) is held in the box end of the spanner, as shown in FIG. 2. Nevertheless, as shown in FIGS. 3 and 4, the nut tends to move out of the box end such that the outer periphery of the nut is apt to be damaged and thus cannot be used anymore. Applicant's U.S. patent application Ser. No. 09/599,206.  proposes an improved spanner for retaining fasteners in place during operation. However, such a spanner cannot be used in a case that the spanner must be passed through, e.g., a nut for driving, e.g., a bolt head to which the nut is engaged when the bolt head is located at a place that is difficult or impossible to access from the other side.